Oh dear.... the follow up

Better lesson, better example. Most of them have got the concept of quartiles. I gave them one more short go at it this morning before letting thme loose on "Mr Schafer's Final Lesson of the Placement Stats Quiz", which was quite good fun. The final question was:
"My head is in the oven and my feet are in the freezer. My average body temperature is absolutely normal." What is wrong with this statement?
Got some interesting, imaginative and articulate responses to that one so I would have left the classroom feeling really good, except that I had to stay behind and supervise the three who hadn't done their homework and were going to do it in lunchtime.